Interpretation of single-well tracer tests using fractional-flow dimensions. Part 1: Theory and mathematical models     

Gerrit van Tonder  Kornelius Riemann  Ingrid Dennis 《Hydrogeology Journal》2002,10(3):351-356

Generalized equations using fractional-flow dimensions were derived to estimate the Darcy and seepage velocities obtained from the point-dilution and the single-well injection-withdrawal field tests conducted in fractured-rock aquifers. Seepage velocities can only be estimated from single-well tests if the hydraulic conductivity and the hydraulic gradient are known a priori. However, if a radial-convergent test is also performed between two boreholes, the kinematic porosity can be estimated and be used to estimate the seepage velocity from the single-well test results. To apply the generalized equations, the flow dimension and the extent of the flow region must be known. Therefore, the generalized radial flow (GRF) model of Barker (1988; a generalized radial flow model for hydraulic tests in fractured rock. Water Resour Res 24(10):1796–1804) is used to estimate the flow dimension because of its wide range of applications. A pumping test performed on the boreholes will yield an estimate of the fractional-flow dimension by applying the GRF model. Electronic Publication  相似文献   

Constraints on the timing of granite emplacement, deformation and metamorphism in the Shamva area, Zimbabwe     

S. Siegesmund  H. Jelsma  J. Becker  G. Davies  P. Layer  E. van Dijk  L. Kater  M. Vinyu 《International Journal of Earth Sciences》2002,91(1):20-34

In order to constrain the temporal relationship between granite (sensu lato) emplacement and metamorphism, isotope work was carried out on the minerals zircon and apatite (U-Pb), garnet (Pb-Pb) and hornblende (Ar-Ar) from wall rock samples in the Shamva area in Zimbabwe. The area, encompassing parts of the Chinamora and Murehwa batholiths and a wedge-shaped greenstone belt segment in between, is commonly quoted in the literature as an example illustrating pluton emplacement processes and deformational models for the Archean. New U-Pb dating of apatite from a boudinaged pegmatite within mafic schists in the batholith-greenstone contact zone has yielded an age of 2619 +28/-24 Ma. This age is interpreted as the best estimation of the intrusion age of this unit, depending on the assumed closure temperature, and provides an upper age limit for the syntectonic emplacement of the now gneissic granites. Pb-Pb dating of late kinematic garnets in cordierite-bearing rocks within the greenstone belt wall rocks gives an age of 2623NJ Ma. Together, this timing of relatively late, syntectonic plutonism and metamorphic mineral growth at ca. 2.62 Ga compares well with existing zircon crystallization ages for felsic volcanics (2645dž Ma, 2643NJ Ma) and post-tectonic porphyritic monzogranites (2601ᆢ Ma). Ar-Ar hornblende ages for mafic schists from different areas within the greenstone belt wall rocks range between 2621 and 2498 Ma and have been interpreted to indicate mixing between metamorphic ages and cooling ages. The data support a geological model whereby volcanism and sedimentation are associated with an early phase of regional deformation at ca. 2.64 Ga, which may have started earlier and lasted longer, and evolves into the voluminous emplacement of granites (now gneissic granites) in the batholiths at approximately 2.62 Ga. Emplacement of post-tectonic tabular monzogranites takes place at ca. 2.60 Ga.  相似文献   

Labour markets in transition. The experiences of women in two border regions of East Germany     

Bettina van Hoven  Carmella Pfaffenbach 《GeoJournal》2002,56(4):261-269

The political turning point in the former GDR and the transformation processes that have been observed since then have significantly affected economic and social structures in the new Federal States. Gender roles, however, were subjected to even more dramatic changes. Whilst many women experienced the employment policies of the GDR era as beneficial, social researchers often designate them as the losers of unification nowadays. This is largely because the abundance of State support measures for employed women and mothers has been drastically reduced and women as a group have been hit hardest by the crisis on the East German labour market. Using two cases (Mecklenburg-Westpommerania and Thuringia), this paper aims to illustrate the impact of the transformation process on the everyday (working) lives of women. We are particularly concerned with a comparative analysis of how women experience and deal with regional disparities in East Germany. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Evidence for compressionally induced high subsidence rates in the Kurile Basin (Okhotsk Sea)   总被引：1，自引：0，他引：1  

Boris V. Baranov  Reinhard Werner  Kaj A. Hoernle  Ira B. Tsoy  Paul van den Bogaard  Igor A. Tararin 《Tectonophysics》2002,350(1)

A combined volcanological, geochemical, paleo-oceanological, geochronological and geophysical study was undertaken on the Kurile Basin, in order to constrain the origin and evolution of this basin. Very high rates of subsidence were determined for the northeastern floor and margin of the Kurile Basin. Dredged volcanic samples from the Geophysicist Seamount, which were formed under subaerial or shallow water conditions but are presently located at depths in excess of 2300 m, were dated at 0.84±0.06 and 1.07±0.04 Ma with the laser ⁴⁰Ar/³⁹Ar single crystal method, yielding a minimum average subsidence rate of 1.6 mm/year for the northeast basin floor in the Quaternary. Trace element and Sr–Nd–Pb isotope data from the volcanic rocks show evidence for contamination within lower continental crust and/or the subcontinental lithospheric mantle, indicating that the basement presently at 6-km depth is likely to represent thinned continental crust. Average subsidence rates of 0.5–2.0 mm/year were estimated for the northeastern slope of the Kurile Basin during the Pliocene and Quaternary through the determination of the age and paleo-environment (depth) of formation of sediments from a canyon wall. Taken together, the data from the northeastern part of the Kurile Basin indicate that subsidence began in or prior to the Early Pliocene and that subsidence rates have increased in the Quaternary. Similar rates of subsidence have been obtained from published studies on the Sakhalin Shelf and Slope and from volcanoes in the rear of the Kurile Arc. The recent stress field of the Kurile Basin is inferred from the analysis of seismic activity, focal mechanism solutions and from the structure of the sedimentary cover and of the Alaid back-arc volcano. Integration of these results suggests that compression is responsible for the rapid subsidence of the Kurile Basin and that subsidence may be an important step in the transition from basin formation to its destruction. The compression of the Kurile Basin results from squeezing of the Okhotsk Plate between four major plates: the Pacific, North American, Eurasian and Amur. We predict that continued compression could lead to subduction of the Kurile Basin floor beneath Hokkaido and the Kurile Arc in the future and thus to basin closure.  相似文献   

Burial of redox-sensitive metals and organic matter in the equatorial Indian Ocean linked to precession     

Delphine PaillerEdouard Bard  Frauke RostekYan Zheng  Richard MortlockAlexander van Geen 《Geochimica et cosmochimica acta》2002,66(5):849-865

Authigenic metals (uranium, cadmium, and molybdenum), organic carbon (OC) and total C₃₇ alkenone (totC₃₇) concentrations were measured for the last 350 kyr in core MD900963, located in the eastern equatorial Arabian Sea. Authigenic metal concentrations on a carbonate-free basis range between 1 and 17 ppm, 0.5 and 6 ppm, and 0.5 and 4 ppm for U, Cd, and Mo, respectively. The profiles are characterized by well-defined 23 kyr cycles between oxic and mildly suboxic conditions. The redox-sensitive metal profiles also follow variations in the concentrations of OC (0.2-0.9%) and alkenones (0.2-6.7 ppm). The coupled variations in inorganic and organic constituents are attributed to a 23-kyr cycle in primary production above site MD900963, as suggested by clear correlations with independent micropaleontologic proxies (primary productivity indices based on foraminifera and coccoliths and fragmentation of foraminiferal shells). The 23-kyr cycles do appear to be primarily driven by productivity rather than changes in bottom water oxygen. Comparison with other records indicates that if this interpretation is correct, productivity variations across much of the Indian Ocean have been dominated by precessional forcing, with high productivity in phase with low summer insolation in the Northern Hemisphere. This interpretation contrasts with the traditional attribution of enhanced productivity in the Indian Ocean with periods of high summer insolation.  相似文献   

Seismic buffer recognition using wavelet-based features and neural classification     

Alwyn Hoffman  Riaan Hoogenboezem  Theo van der Merwe  Tonie Tollig 《Geophysical Prospecting》2002,50(4):361-371

One of the first operations in a seismic signal processing system applied to earthquake data is to distinguish between valid and invalid records. Since valid signals are characterized by a combination of their time and frequency properties, wavelets are natural candidates for describing seismic features in a compact way. This paper develops a seismic buffer pattern recognition technique, comprising wavelet-based feature extraction, feature selection based on the mutual information criterion, and neural classification based on feedforward networks. The ability of the wavelet transform to capture discriminating information from seismic data in a small number of features is compared with alternative feature reduction techniques, including statistical moments. Three different variations of the wavelet transform are used to extract features: the discrete wavelet transform, the single wavelet transform and the continuous wavelet transform. The mutual information criterion is employed to select a relatively small set of wavelets from the time–frequency grid. Firstly, it is determined whether wavelets can capture more informative data in an equal number of features compared with other features derived from raw data. Secondly, wavelet-based features are compared with features selected based on prior knowledge of class differences. Thirdly, a technique is developed to optimize wavelet features as part of the neural network training process, by using the wavelet neural network architecture. The automated classification techniques developed in this paper are shown to perform similarly to human operators trained for this function. Wavelet-based techniques are found to be useful, both for preprocessing of the raw data and for extracting features from the data. It is demonstrated that the definition of wavelet features can be optimized using the classification wavelet network architecture.  相似文献   

Competitive Adjustment and Advancement in Global Commodity Chains II: The Case of the Singapore Garment Industry     

Leo van Grunsven  & Floor Smakman 《Singapore journal of tropical geography》2002,23(1):70-92

This is the second part of a contribution to the debate on the possibilities of leveraging economic globalisation — through incorporation in international production networks and global commodity chains (GCCs) — as a strategy for developing countries to industrialise and advance their position in the world economy. In the first part, we analysed the experience of the East Asian apparel industry and addressed the issues of sustaining positions, upgrading to more rewarding roles, and advancing to less dependent positions within production networks and GCCs. We developed an analytical framework at both the firm and industry levels, and subsequently identified alternative firm- and industry-level strategies and trajectories. The present paper deals with these issues in the context of the Singapore apparel industry. Based on extensive empirical research, we demonstrate that although the East Asian experience of upgrading and repositioning within the GCC is to some extent emulated in the case of the Singapore apparel industry, the outcomes have been less favourable in terms of the depth, extent and strength of these trajectories. The differing outcomes can be explained in terms of different (systemic) conditions in the Singapore business environment, including the agency of local players, the geography of sourcing networks, and the role of the state and prevailing business attitudes. Our conclusions merit continued attention in both research and policy circles on the development of capabilities at the firm level, and the role of local business and institutional environments in local industry development processes under globalisation.  相似文献   

Finite-difference modelling of two-dimensional elastic wave propagation in cracked media     

Vincent A. van Antwerpen  Wim A. Mulder  Gérard C. Herman 《Geophysical Journal International》2002,149(1):169-178

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Data and model uncertainty estimation for linear inversion   总被引：1，自引：0，他引：1  

Kasper van Wijk  John A. Scales  William Navidi  Luis Tenorio 《Geophysical Journal International》2002,149(3):625-632

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Patch use and exploratory movements of a resident houbara bustard in northern Saudi Arabia     

Yolanda van Heezik  Philip J. Seddon 《Journal of Arid Environments》2002,50(4):683

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